Oxide sintered body, production method therefor, target, and transparent conductive film

ABSTRACT

A target for sputtering which enables to attain high rate film-formation of a transparent conductive film suitable for a blue LED or a solar cell. A oxide sintered body includes an indium oxide and a cerium oxide, and one or more oxide of titanium, zirconium, hafnium, molybdenum and tungsten. The cerium content is 0.3 to 9% by atom, as an atomicity ratio of Ce/(In+Ce+M), the M element content is equal to or lower than 1% by atom, as an atomicity ratio of M/(In+Ce+M), and the total content of cerium and the M element is equal to or lower than 9% by atom, as an atomicity ratio of (Ce+M)/(In+Ce+M). The oxide sintered body has an In 2 O 3  phase of a bixbyite structure has a CeO 2  phase of a fluorite-type structure finely dispersed as crystal grains having an average particle diameter of equal to or smaller than 3 μm.

TECHNICAL FIELD

The present invention relates to an oxide sintered body and a productionmethod therefor, a target, and a transparent conductive film, and inmore detail, the present invention relates to a target for sputteringwhich enables to attain high rate film-formation of a transparentconductive film suitable for a blue LED or a solar cell, and anoduleless film-formation, an oxide sintered body most suitable forobtaining the same, and a production method thereof.

BACKGROUND ART

A transparent conductive film, because of having high conductivity andhigh transmittance in a visible light region, has been utilized in anelectrode or the like, for a solar cell or a liquid crystal displayelement, and other various light receiving elements, as well as a heatray reflection film for an automotive window or construction use, anantistatic film, and a transparent heat generator for variousanti-fogging for a refrigerator showcase and the like.

As a well known practical transparent conductive film, there has beenincluded a thin film of tin oxide (SnO₂)-type, zinc oxide (ZnO)-type,indium oxide (In₂O₃)-type. As the tin oxide-type, the one containingantimony as a dopant (ATO), or the one containing fluorine as a dopant(FTO) has been utilized, and as the zinc oxide-type, the one containingaluminum as a dopant (AZO), or the one containing gallium as a dopant(GZO) has been utilized. However, the transparent conductive film mostwidely used industrially is the indium oxide-type. Among them, indiumoxide containing tin as a dopant is called an ITO (Indium-Tin-Oxide)film, and has been utilized widely, because, in particular, a film withlow resistance can be obtained easily.

The transparent conductive film with low resistance is suitably usedwidely in a surface element or a touch panel or the like, of such as fora solar cell, a liquid crystal, an organic electroluminescence and aninorganic electroluminescence. As a production method for thesetransparent conductive films, a sputtering method or an ion platingmethod has been used often. This sputtering method is an effectivemethod in film-formation of a material with low vapor pressure, or whencontrol of precise film thickness is required, and because of verysimple and easy operation thereof, it has been widely used industrially.

In a sputtering method, a target for sputtering is used as a rawmaterial of a thin film. The target is a solid containing a metalelement constituting the thin film to be formed, and a sintered bodysuch as a metal, a metal oxide, a metal nitride, a metal carbide, or, incertain cases, a single crystal is used. In this method, in general,after making high vacuum once with a vacuuming apparatus, rare gas(argon or the like) is introduced, and under a gas pressure of equal toor lower than about 10 Pa, a substrate is set as an anode and a targetis set as a cathode to generate glow discharge between them and generateargon plasma, and argon cations in the plasma are collided with thetarget of the cathode, and particles of the target component flickedthereby are deposited on the substrate to form a film.

A sputtering method is classified by a generation method of argonplasma, and a method using high frequency plasma is called a highfrequency sputtering method, and a method using direct-current plasma iscalled a direct-current sputtering method.

In general, a direct-current sputtering method has been utilizedindustrially in a wide range, because it provides higher film-formationrate and lower cost of power source facility and simpler film-formationoperation, as compared with the high frequency sputtering method.However, the direct-current sputtering method has a disadvantage ofrequiring use of a conductive target, as compared with the highfrequency sputtering method, which can provide film-formation even byusing an insulating target.

Film-formation rate of a sputtering has close relation to chemical bondof a target substance. Because a sputtering is a phenomenon that argoncations having a kinetic energy are collided to the target surface, anda substance of a target surface is flicked by receiving energy, theweaker inter-ionic bond or inter-atomic bond of the target substanceincreases the more probability of jumping out by sputtering.

In film-formation of a transparent conductive film of an oxide such asITO by using a sputtering method, there are a method for film-formationof an oxide film by a reactive sputtering method in mixed gas of argonand oxygen, by using an alloy target (an In—Sn alloy in the case of theITO film) of metals constituting the film, and a method forfilm-formation of an oxide film by a reactive sputtering method forperforming a sputtering in mixed gas of argon and oxygen, by using anoxide sintered body target (an In—Sn—O sintered body in the case of theITO film) composed of an oxide of metal constituting the film.

Among these, in a method for using the alloy target, relatively highamount of oxygen gas is supplied during sputtering, however, becausedependence of film-formation rate or film characteristics (specificresistance, transmittance) on amount of oxygen gas to be introducedduring film-formation is extremely high, it is difficult to producestably a transparent conductive film having a constant film thickness orcharacteristics.

On the other hand, a method for using the metal oxide target supplies apart of oxygen supplied to the film from the target by sputtering, andthus residual deficient oxygen amount is supplied as oxygen gas, anddependence of characteristics (specific resistance, transmittance or thelike) of the film on film-formation rate or oxygen gas amount to beintroduced during film-formation is smaller than the case of using thealloy target, and because the transparent conductive film havingconstant film thickness and characteristics can be produced stably, amethod for using the oxide target has been adopted industrially.

From such a background, in the case of mass production of thetransparent conductive film by film-formation using the sputteringmethod, the direct-current sputtering method using the metal oxidetarget has been mainly adopted. Here, in consideration of productivityor production cost, characteristics of the oxide target duringdirect-current sputtering become important. That is, such an oxidetarget is useful that provides higher film-formation rate in the case ofcharging the same power. Still more, because film-formation rate becomesthe higher, when the higher direct-current sputtering is charged, suchan oxide target becomes useful industrially that is capable offilm-forming stably without generation of target cracking or abnormaldischarge caused by arcing due to nodule generation, even when highdirect-current power is charged.

Here, the nodule means a black precipitate (protruded substance)generating at an erosion part of the target surface (meaning a site ofthe target being sputtered), excluding a very small part at the deepestpart of erosion, when sputtering of the target proceeds. In general, thenodule is said not to be a deposition of a foreign flying substance or areaction product at the surface, but a digging residue by sputtering.The nodule causes abnormal discharge such as arcing, and it has beenknown that arcing is suppressed by reducing the nodule (refer toNON-PATENT LITERATURE 1). Therefore, for performing stablefilm-formation, use of such an oxide target is necessary that does notgenerate the nodule, that is, a digging residue by sputtering.

On the other hand, the ion plating method is a method for evaporating ametal or a metal oxide by resistance heating or electron-beam heating,under a pressure of about 10⁻³ to 10⁻² Pa, and still more activating theevaporated substance using plasma and reaction gas (oxygen) to depositit on a substrate. Also as for the target for ion plating (it may alsobe called a tablet of pellet) to be used in forming the transparentconductive film, similarly as in the target for sputtering, use of anoxide tablet enables to more stably produce a transparent conductivefilm having constant film thickness and constant characteristics. Theoxide tablet is required to evaporate uniformly, and it is preferablethat a substance having stable chemical bond and difficult to beevaporated is not present together with a substance which is present asa main phase and easily evaporated.

As described above, it can be said that in order to form the transparentconductive film of an oxide such as ITO by the direct-current sputteringmethod or the ion plating method, such an oxide target is important thatenables stable film-formation without generation of abnormal dischargecaused by arcing or the like due to nodule generation.

By the way, many of the transparent conductive films such as ITO film,formed by the above process, are n-type degenerated semiconductors, andlargely contribute to enhance conductivity of electrons of carriers.Therefore, conventionally, in order to make low resistance of the ITOfilm, carrier electron concentration has been made to increase as highas possible.

The ITO film has been known to have a crystallization temperature ofgenerally about 190 to 200° C., and bordering on this temperature, anamorphous film or a crystalline film is formed. For example, in the caseof film-formation by a sputtering method while maintaining the substrateat room temperature, the amorphous film is obtained, because thermalenergy required in crystallization cannot be given. On the other hand,in the case where a substrate temperature is equal to or higher thancrystallization temperature , for example, about 300° C., thecrystalline film is formed.

In the amorphous film and the crystalline film of ITO, generationmechanism of carrier electrons is different. In general, in the case ofthe amorphous film, nearly all of the carrier electrons are generated byoxygen deficiency. On the other hand, in the case of the crystallinefilm, generation of the carrier electrons is expected by not only oxygendeficiency but also tin doping effect.

Indium oxide takes a crystal structure called bixbyite of a stable cubicsystem crystal phase, under normal pressure or pressure lower than that.By substitution of a lattice point of tri-valent indium in the bixbyitestructure with tetra-valent tin, the carrier electrons are generated.Tin is an element which is capable of increasing carrier electronconcentration most, as a dopant, and it has been known that the additionof 10% by weight as converted to tin oxide is capable of making lowresistance most. That is, by converting the ITO film to a crystallinefilm, carrier electrons are generated in a large quantity by both ofoxygen deficiency and the tin dopant, and therefore it is possible toform a film showing lower electric resistance as compared with anamorphous film having only oxygen deficiency.

However, in an LED (light Emitting Diode) or a solar cell whose progresshas been significant in recent years, there has emerged a case requiringcharacteristics which is difficult to attain by ITO. As one examplethereof, in a blue LED, to enhance light extraction efficiency, highrefractive index of the transparent conductive film has been necessaryfor blue light at the vicinity of a wavelength of 460 nm. As a lightemitting layer of the blue LED, a gallium nitride layer is used. As anoptical characteristics of the gallium nitride layer, refractive indexas high as about 2.4 is included. In order to enhance efficiency oflight extraction from the light emitting layer, it is necessary toenhance consistency of refractive indexes of the transparent conductivefilm and the gallium nitride layer, and the transparent conductive filmis required to have a refractive index of as near as 2.4. Refractiveindex is a value specific to a substance, and generally known refractiveindex of indium oxide is as low as 1.9 to 2.0. In addition, thetransparent conductive film is required to have low surface resistance.It is because current diffusion is not sufficient in a film surfacedirection, as electrical characteristics of the gallium nitride layer.However, when it is tried to decrease electric resistance by increasingcarrier electron concentration, refractive index of the indiumoxide-type transparent conductive film becomes lowered further than 1.9to 2.0 to 1.8 to 1.9. As described above, because the ITO film is amaterial having significantly increased carrier electron concentrationowing to tin as a dopant, trying to obtain a crystalline film with sucha low resistance results in decreasing refractive index, and this hasbeen a problem to be solved.

In addition, other than refractive index or specific resistance,characteristics such as patterning property by wet etching or the like,superior than that of the ITO film, is required. Also in the above blueLED, such a process is preferable that makes low resistance byperforming patterning by wet etching using a weak acid on the amorphoustransparent conductive film formed at low temperature, and then by heattreatment under non-oxidative atmosphere to crystallize the amorphoustransparent conductive film. By using this process, it is possible toform a transparent electrode having highly fine patterning.

As other application examples of the transparent conductive film, thereis a solar cell. In the case of using it as a surface electrode of asolar cell, when the transparent conductive film has high transmittanceof not only visible light but also infrared light, solar light can betaken in efficiently. The ITO film is capable of decreasing specificresistance, however, because of high carrier electron concentration,there was a problem of high reflectance or absorption of infrared light,and thus decreasing transmittance.

In addition, in the case of using it as a part of a rear surfaceelectrode, there may be the case of using a transparent conductive filmhaving enhanced refractive index, for performing adjustment ofrefractive index of the whole module, aiming at enhancing incorporationefficiency of solar light, however, also in this case, the ITO film wasinsufficient because of the same reason as in a blue LED application.However, in a solar cell application, it is not required suchhigh-definition patterning by wet etching using a weak acid, that isrequired in the blue LED.

As one method for enhancing refractive index of the indium oxide-typetransparent conductive film, there is a method for adding an oxidehaving high refractive index.

In PATENT LITERATURE 1, there has been described a sputtering target,which is capable of efficiently forming a transparent thin film withsuperior moisture-proof property, on a silver-type thin film by asputtering method, and gives little damage to the above silver-type thinfilm, and there has been proposed a sputtering target composed of aconductive transparent metal oxide containing an oxide of a metalelement substantially not having a solid solution region with silver,wherein content ratio of the above metal substantially not having asolid solution region with silver, is 5 to 40% by atom relative to themetal element of the conductive transparent metal oxide. Specifically,it has been described that containing of at least a titanium element ora cerium element is preferable, as the metal element substantially nothaving a solid solution region with silver, and as a metal elementsimilarly applicable, there has been included a zirconium element, ahafnium element, a tantalum element. In addition, there has beendescribed that indium oxide is preferable as the conductive transparentmetal oxide.

In addition, in PATENT LITERATURE 1, there has been described thatbecause the metal oxide of the titanium element or the cerium element,which is the metal element substantially not having a solid solutionregion with silver, has a high refractive index of equal to or higherthan 2.3, and as said high refractive index material, total content rateof the titanium element and the cerium element is 5 to 40% by atomrelative to the metal element of the conductive transparent metal oxide,it is possible to increase refractive index of the transparentconductive film, formed by using this sputtering target, up to about 2.1to 2.3.

In addition, in PATENT LITERATURE 2, there has been proposed asputtering target of a sintered body of a mixed oxide applicable infilm-forming a transparent thin film of a conductive film with acomposition sandwiching the silver-type thin film. In film-formation ofthe transparent thin film of the conductive film with a configurationsandwiching the silver-type thin film, in order to be able toeffectively perform film-formation of the transparent thin film withsuperior moisture-proof property, and also to obtain a sputtering targetwhere the above silver-type thin film little receives damage in thisfilm-formation, specifically, a sintered body of the mixed oxide havingcontained tin oxide and/or titanium oxide in an amount lower than mixingratio of each substrate, to a mixed oxide having indium oxide and ceriumoxide as the substrate, is used. That is, similarly as in PATENTLITERATURE 1, because cerium oxide has high refractive index, alsorefractive index of the mixed oxide of indium oxide and cerium oxidebecomes high, accompanying with addition ratio of cerium oxide.

Still more, because in the mixed oxide of indium oxide and cerium oxide,cerium oxide does not have sufficient conductivity, conductivity of atarget using a sintered body of the mixed oxide abruptly decreasesaccompanying with increase in mixing ratio of cerium oxide, and thusproviding a target with low conductivity, which makes difficultfilm-formation by a direct-current sputtering method.

As described above, according to PATENT LITERATUREs 1 and 2, it isexpected to increase refractive index of the transparent thin film,formed by using this sputtering target, up to about 2.1 to 2.3, becauseefficient formation of the transparent thin film with superiormoisture-proof property is possible by a sputtering method on thesilver-type thin film, or because a metal oxide of a titanium element ora cerium element has a high refractive index of equal to or higher than2.3. However, as described above, in the case of mass production of thetransparent conductive film by film-formation using a direct-currentsputtering method, in view of industrial usefulness of such an oxidetarget that is capable of stable film-formation without generation oftarget cracking or abnormal discharge caused by arcing due to nodulegeneration, even when high direct-current power is charged, it isnecessary that nodule generation causing the above arcing is suppressed,or splash in an ion plating method is suppressed, when condition toincrease film-formation rate, by increasing sputtering voltage or thelike, is selected, but investigation on a texture or the like of theoxide sintered body enabling it has not been performed at all.

That is, there has not been considered to the point of industriallyrequired characteristics, relating to the oxide sintered body to obtaina target applicable to stable film-formation of the above transparentconductive film.

Still more, in PATENT LITERATUREs 1 and 2, although there has beeninvestigated a method for production a sintered body to obtain a target,or a method for enhancing conductivity, by the simple addition of tinoxide or titanium oxide, there has not been investigated at all a methodfor enhancing density of a sintered body by detailed analysis andcontrol of a texture of the oxide sintered body containing indium andcerium as oxides; or a method for avoiding arcing in film-formationusing the above sputtering method, or splash in film-formation using theion plating method. In addition, as for the case where a crystallinetransparent conductive film was formed, there has not been investigatedat all influence of tin oxide or titanium oxide, which is the additionelement, on refractive index of the transparent conductive film.

On the other hand, in PATENT LITERATURE 3, there has been proposed anamorphous transparent conductive thin film which is extremely smooth andhas a high work function, an oxide sintered body which is capable offorming stably said transparent conductive thin film, and a sputteringtarget using the same, and there has been described that it is desirablethat said oxide sintered body contains 3% by mass to 20% by mass ofcerium, 0.1% by mass to 4% by mass of tin, and 0.1% by mass to 0.6% bymass of titanium, and the remaining is substantially composed of indiumand oxygen, and still more cerium, tin and titanium make a solidsolution in an indium site, sintering density is equal to or higher than7.0 g/cm³, and average crystal grain diameter is equal to or smallerthan 3 μm.

Also in this PATENT LITERATURE 3, there has not been investigated at allenhancement of refractive index of the crystalline transparentconductive film formed by using said sputtering target. In particular,there has not been referred at all to influence of tin on decrease inrefractive index.

Still more, as for said oxide sintered body, average particle diameterof a crystal grain of indium oxide, where cerium, tin and titanium makea solid solution in an indium site, is controlled at equal to or smallerthan 3 μm, aiming at suppressing sintering crack during sputtering andnodule generation at that part, however, there has not been investigatedat all a problem that cerium does not make a solid solution in indiumoxide, and is present as crystal grains of cerium oxide, which becomes astarting point of a nodule.

In addition, in PATENT LITERATURE 4, there has been described asputtering target characterized in that, in a sputtering target composedof indium oxide and cerium oxide, in the case of observing crystal peaksusing X-ray diffraction, presence of peaks derived from indium oxide andcerium oxide are observed, and in performing EPMA measurement, diameterof a cerium oxide particle dispersed in indium oxide is found to beequal to or smaller than 5 μm.

This PATENT LITERATURE 4 is a sputtering target composed of indium oxideand cerium oxide, and has not investigated at all enhancement ofrefractive index and decrease in resistance of a crystalline transparentconductive film formed by using said sputtering target composed ofindium oxide and cerium oxide, and not added with titanium or the like.In particular, there has not been referred at all to influence of tin ondecreasing refractive index.

As described above, in conventional technology relating to an oxidesintered body containing indium and cerium having low specificresistance and high refractive index, sufficient investigation has notbeen performed on nodule suppression in sputtering film-formation, orsplash prevention or the like in ion plating film-formation, whichbecomes important in view of mass production of a crystallinetransparent conductive film, and it has been desired emergence of anoxide sintered body containing indium and cerium, which has solved theseproblems.

CITATION LIST Patent Literature

-   PATENT LITERATURE 1: JP-A-8-260134-   PATENT LITERATURE 2: JP-A-9-176841-   PATENT LITERATURE 3: JP-A-2005-320192-   PATENT LITERATURE 4: JP-A-2005-290458

Non-Patent Literature

-   NON-PATENT LITERATURE 1: “Technology of a transparent conductive    film (the second Revised version)”, Ohmsha, Ltd., published on Dec.    20, 2006, pages 238 to 239-   NON-PATENT LITERATURE 2: “New development of a transparent    conductive film”, CMC, published on Mar. 1, 1999, pages 117 to 125

SUMMARY OF INVENTION Technical Problem

It is an object of the present invention to provide the target forsputtering which is capable of attaining high film-formation rate of thecrystalline transparent conductive film having low specific resistanceand high refractive index, along with noduleless in sputteringfilm-formation, the oxide sintered body most suitable for obtaining it,and the production method therefor.

Solution to Problem

The present inventors have studied in detail on influence of acompositional phase and a texture of the oxide sintered body onproduction conditions such as film-formation rate thereof and the like,or nodule generation causing arcing, by preparing many oxide sinteredbody samples by changing the compositional phase and the texture of theoxide sintered body containing oxides of indium and tin as maincomponents, and still more an oxide of such as titanium or the like, andforming the oxide transparent conductive film by a sputtering method,using this as a raw material.

As a result, we have discovered that nodule generation causing arcingcan be suppressed more, as compared with conventional cases, even in thecase of enhancing film-formation rate by increasing charged power informing the above transparent conductive film on a substrate, by (1)setting cerium content at 0.3 to 9% by atom, as an atomicity ratio ofCe/(In+Ce+M), the content of the M element at equal to or lower than 1%by atom, as an atomicity ratio of M/(In+Ce+M), and total content ofcerium and the M element at equal to or lower than 9% by atom, as anatomicity ratio of (Ce+M)/(In+Ce+M), in the oxide sintered bodycontaining indium and cerium and still more at least one or more kindsof an metal element (M element) selected from the metal element groupconsisting of titanium, zirconium, hafnium, molybdenum and tungsten, asan oxide, as well as (2) by composing the above oxide sintered body withsubstantially an In₂O₃ phase of a bixbyite structure and a CeO₂ phase ofa fluorite-type structure, and controlling the average particle diameterof crystal grains composed of a CeO₂ phase, dispersing in the In₂O₃phase, at equal to or smaller than 3 μm, and as a result, thecrystalline transparent conductive film having low specific resistanceand high refractive index can be obtained efficiently and stably, andhave thus completed the present invention.

That is, according to a first aspect of the present invention, there isprovided a oxide sintered body comprising an indium oxide and a ceriumoxide, and further comprising, as an oxide, at least one or more kindsof an metal element (M element) selected from the metal element groupconsisting of titanium, zirconium, hafnium, molybdenum and tungsten,wherein the cerium content is 0.3 to 9% by atom, as an atomicity ratioof Ce/(In+Ce+M), the M element content is equal to or lower than 1% byatom, as an atomicity ratio of M/(In+Ce+M), and the total content ofcerium and the M element is equal to or lower than 9% by atom, as anatomicity ratio of (Ce+M)/(In+Ce+M), characterized in that: said oxidesintered body has an In₂O₃ phase of a bixbyite structure as a maincrystal phase, has a CeO₂ phase of a fluorite-type structure finelydispersed as crystal grains having an average particle diameter of equalto or smaller than 3 μm, as a second phase

In addition, according to a second aspect of the present invention,there is provided the oxide sintered body, characterized in that, in thefirst aspect, X-ray diffraction peak intensity ratio (I) , defined bythe following formula, is equal to or lower than 25%:I=[CeO₂ phase (111)/In₂O₃ phase (222)]×100 [%]

In addition, according to a third aspect of the present invention, thereis provided the oxide sintered body according to claim 1, characterizedin that, in the first aspect, the M element is titanium.

In addition, according to a fourth aspect of the present invention,there is provided the oxide sintered body, characterized by, in thefirst aspect, not comprising tin

In addition, according to a fifth aspect of the present invention, thereis provided a production method for a oxide sintered body obtained byadding and mixing oxide powder of at least one or more kinds of an Melement selected from the M metal element group consisting of titanium,zirconium, hafnium, molybdenum and tungsten, to raw material powdercomprising indium oxide powder and cerium oxide powder, and then moldingthe mixed powder, and sintering the molding by a normal pressuresintering method, or molding and sintering the mixed powder by a hotpress method, characterized in that average particle diameter of the rawmaterial powder is adjusted to equal to or smaller than 1.5 μm, theoxide powder is mixed to said raw material powder, then molded, and theresultant molding is sintered, so that the oxide sintered body aftersintering has an In₂O₃ phase of a bixbyite-type structure, as a maincrystal phase, has a CeO₂ phase of a fluorite-type structure finelydispersed as crystal grains having an average particle diameter of equalto or smaller than 3 μm, as a second phase.

In addition, according to a sixth aspect of the present invention, thereis provided the production method for the oxide sintered body,characterized in that, in the fifth aspect, the oxide sintered body fora target to be used in forming a transparent conductive film by asputtering method is obtained by sintering the molding by a normalpressure sintering method, under atmosphere containing oxygen gas, at asintering temperature of 1250 to 1650° C., for a sintering time of 10 to30 hours.

In addition, according to a seventh aspect of the present invention,there is provided the production method for the oxide sintered body,characterized in that, in the fifth aspect, the oxide sintered body fora target to be used in forming a transparent conductive film by asputtering method is obtained by molding and sintering the mixed powderby a hot press method, at a temperature of 700 to 950° C. for 1 to 10hours, under a pressure of 2.45 to 29.40 MPa, under inert gas atmosphereor in vacuum.

On the other hand, according to an eighth aspect of the presentinvention, there is provided a target for sputtering obtained byfabricating the oxide sintered body in any of the first to the fourthaspects wherein density of the oxide sintered body is equal to or higherthan 6.3 g/cm³.

Still more, according to a ninth aspect of the present invention, thereis provided, a transparent conductive film characterized by being formedon a substrate by a sputtering method, using the target of the eighthaspect of the present invention.

Advantageous Effects of Invention

Because the oxide sintered body containing indium and cerium, still morecontaining at least one or more kinds of an metal element (M element)selected from the metal element group consisting of titanium, zirconium,hafnium, molybdenum and tungsten, of the present invention, has thecerium content of 0.3 to 9% by atom, as an atomicity ratio ofCe/(In+Ce+M), the M element content of equal to or lower than 1% byatom, as an atomicity ratio of M/(In+Ce+M), and the total content ofcerium and the M element of equal to or lower than 9% by atom, as anatomicity ratio of (Ce+M)/(In+Ce+M), and contains the In₂O₃ phase of abixbyite-type structure, as a main crystal phase, and the CeO₂ phase ofa fluorite-type structure, as a second phase, is finely dispersed ascrystal grains with an average particle diameter of equal to or smallerthan 3 μm, nodule generation causing arcing can be suppressed, even inincreased film-formation rate, in obtaining an oxide transparentconductive film using said oxide sintered body by a sputtering method.Thereby, it is possible to shift to film-formation condition withincreased film-formation rate, and mass production of the transparentconductive film is possible. As a result, the crystalline transparentconductive film having low specific resistance and high refractiveindex, containing indium and cerium, and at least one or more kinds ofthe metal element (M element) selected from the metal element groupconsisting of titanium, zirconium, hafnium, molybdenum and tungsten, canbe obtained efficiently, which is extremely useful industrially.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a photo showing a secondary electron image by a scanningelectron microscope (SEM), and surface analysis result by an energydispersive X-ray analysis method (EDS) of the cross-section of an oxidesintered body containing cerium in a content of 9% by atom, as anatomicity ratio of Ce/(In+Ce), as an example of an In₂O₃ phase of a maincrystal phase, wherein a crystal grain of a CeO₂ phase is finelydispersed .

FIG. 2 is a chart showing an X-ray diffraction measurement result of theoxide sintered body of Reference Example 1, containing indium and ceriumas oxides, wherein the cerium content is 9% by atom, as an atomicityratio of Ce/(In+Ce), and being composed of an In₂O₃ phase of abixbyite-type structure and a CeO₂ phase of a fluorite-type structure.

FIG. 3 is a graph showing an arcing generation state in sputtering usingthe oxide sintered body of Comparative Example 3.

FIG. 4 is a chart showing an X-ray diffraction measurement result of theoxide sintered body of Example 3, containing indium, cerium and titaniumas oxides, wherein the cerium content is 4% by atom, as an atomicityratio of Ce/(In+Ce+Ti) and the titanium content is 1% by atom, as anatomicity ratio of Ti/(In+Ce+Ti) , and being composed of an In₂O₃ phaseof a bixbyite-type structure and a CeO₂ phase of a fluorite-typestructure.

FIG. 5 is a photo showing a secondary electron image by a scanningelectron microscope (SEM) , and surface analysis result by an energydispersive X-ray analysis method (EDS) of the cross-section of an oxidesintered body of Example 3, containing cerium in a content of 4% byatom, as an atomicity ratio of Ce/(In+Ce+Ti) and containing titanium ina content is 1% by atom, as an atomicity ratio of Ti/(In+Ce+Ti) , as anexample of an In₂O₃ phase of a main crystal phase, wherein a crystalgrain of a CeO₂ phase is finely dispersed.

DESCRIPTION OF EMBODIMENTS

Explanation will be given below in detail on the oxide sintered body,the production method therefor, the target and the transparentconductive film, of the present invention, with reference to drawings.

1. An Oxide Sintered Body

In the present invention, it is preferable that the oxide sintered bodycontaining the indium oxide and the cerium oxide, further the oxide ofat least one or more kinds of the metal element (M element) selectedfrom the metal element group consisting of titanium, zirconium, hafnium,molybdenum and tungsten, has a specific phase structure, wherein thecerium content is 0.3 to 9% by atom, as an atomicity ratio ofCe/(In+Ce+M), the M element content is equal to or lower than 1% byatom, as an atomicity ratio of M/(In+Ce+M), and the total content ofcerium and M element is equal to or lower than 9% by atom, as anatomicity ratio of (Ce+M)/(In+Ce+M), and the M element is particularlypreferably titanium.

As described above, conventionally, a target for sputtering aiming atforming a transparent conductive film composed of oxides containingindium and cerium has been proposed, however, because there has not beeninvestigated sufficiently, as for the oxide sintered body containingindium and cerium to be a material thereof, on optimization of thecompositional phase and the texture, or the like, of said oxide sinteredbody, nodule generation at the target surface causing arcing cannot besuppressed, and thus it was impossible to produce the transparentconductive film in high rate. In the present invention, the oxidesintered body containing indium and cerium has been investigated indetail, in view of the compositional phase and the texture thereof, toclarify influence on film-formation rate of the oxide transparentconductive film, or on nodule generation at the target surface causingarcing in film-formation.

The oxide sintered body of the present invention contains the indiumoxide and the cerium oxide, and still more at least one or more kinds ofthe metal element (M element) selected from the metal element groupconsisting of titanium, zirconium, hafnium, molybdenum and tungsten, asan oxide, wherein the cerium content is 0.3 to 9% by atom, as anatomicity ratio of Ce/(In+Ce+M) , the M element content is equal to orlower than 1% by atom, as an atomicity ratio of M/(In+Ce+M), and thetotal content of cerium and the M element is equal to or lower than 9%by atom, as an atomicity ratio of (Ce+M)/(In+Ce+M), and the In₂O₃ phaseof a bixbyite-type structure is a main crystal phase, and, as a secondphase, a CeO₂ phase of a fluorite-type structure is finely dispersed ascrystal grains having an average particle diameter of equal to orsmaller than 3 μm.

(a) Composition

As for the oxide sintered body of the present invention, it is necessarythat the cerium content is 0.3 to 9% by atom, as an atomicity ratio ofCe/(In+Ce+M) , the M element content is equal to or lower than 1% byatom, as an atomicity ratio of M/(In+Ce+M), and the total content ofcerium and the M element is equal to or lower than 9% by atom, as anatomicity ratio of (Ce+M)/(In+Ce+M), so that the crystalline transparentconductive film having low specific resistance and high refractive indexis obtained, by a sputtering method.

In the case where the cerium content of the oxide sintered body is below0.3% by atom, as an atomicity ratio of Ce/(In+Ce+M), carrier electronsminimum required are not generated in the transparent conductive filmformed using this as a raw material, and is thus not preferable. For thetransparent conductive film formed using the oxide sintered body as araw material to show low specific resistance due to high mobility, it isnecessary to generate a small amount of carrier electrons by doping ofcerium, in addition to carrier electrons generated by oxygen deficiency.

On the other hand, in the case where cerium content of the oxidesintered body is over 9% by atom, as an atomicity ratio of Ce/(In+Ce+M),ratio of the CeO₂ phase of a fluorite-type structure dispersed in theoxide sintered body results in being increased, and the CeO2 phasebecomes to have higher electric resistance and lower film-formationrate, as compared with the In₂O₃ phase, and thus production efficiencydecreases industrially. In addition, the excess addition of Ce increasesspecific resistance of the crystalline transparent conductive filmformed, and makes it difficult to obtain equal to or lower than 8×10⁻⁴Ω·cm minimum required in using as a transparent electrode of a blue LEDor a solar cell.

Reason for making contain at least one or more kinds of the M metalelement selected from the metal element group consisting of titanium,zirconium, hafnium, molybdenum and tungsten, as an oxide of the Melement, into the transparent conductive film containing indium andcerium, is to generate carrier electrons stably. As described above,cerium is possible to generate carrier electrons, however, becausegeneration effect thereof is very small, which inhibits stablegeneration, which may result in the case where amount of carrierelectrons minimal required cannot be obtained. On the other hand, when Melement content is equal to or lower than 1% by atom, as an atomicityratio relative to total metal elements M element, generation effect ofcarrier electrons becomes several times high, as compared with cerium,and carrier electrons can be obtained stably, and thus amount of carrierelectrons required can be generated by only a trance amount of theaddition. It should be noted that, because it is necessary to decreasethe addition amount of cerium to compensate the addition of the Melement, effect of more decreasing specific resistance can be obtained,although refractive index decreases a little. This effect is valid alsoin a combination of two or more kinds of elements selected from theabove element group.

In addition, because tin has far higher generation effect of carrierelectrons, when added to indium oxide, tin should not be contained. Itis not preferable to make contain also elements such as silicon,germanium, antimony, bismuth and tellurium and the like, by the samereason, although the above effect thereof is a little inferior, ascompared with tin. However, as for unavoidable impurities of amountswhich does not influence to the above characteristics, it does notapply.

(b) A Generated Phase and a Form Thereof

It is necessary that the oxide sintered body of the present inventionshould have not only the above composition rage, but also the texturethereof should have the In₂O₃ phase of a bixbyite structure, as a maincrystal phase, and the CeO₂ phase of a fluorite-type structure should befinely dispersed, as a second phase, as crystal grains having an averageparticle diameter of equal to or smaller than 3 μm.

In the In₂O₃ phase of a bixbyite structure as the main phase, ceriumseldom makes a solid solution. On the other hand, indium seldom makes asolid solution also in the CeO₂ phase of a fluorite-type structure of adispersed phase. However, in the both phases, a part of indium may besubstituted with cerium in a non-equilibrium way, or a part of ceriummay be substituted with indium, or there may be contained some shiftsfrom a stoichiometric composition, metal element deficiency or oxygendeficiency.

In the above PATENT LITERATURE 3, there has been described that cerium,tin and titanium make a solid solution in an indium site of the In₂O₃phase which is the oxide sintered body. Originally, cerium seldom makesa solid solution in the In₂O₃ phase, however, in the case of the PATENTLITERATURE 3, it is estimated that cerium becomes easy to make a solidsolution due to containing mainly tin. In addition, also in the abovePATENT LITERATUREs 1 and 2, it is estimated that cerium became easy tomake a solid solution similarly, because tin or titanium is containingin relatively high compositional ratio as compared with cerium, in mostExamples. However, in the case of adding cerium in such a large quantityas over the composition range of the present invention, it does notapply, and for example, a mixed oxide containing any of In, Ce, Sn andTi may be formed as an another phase.

In addition, as for the oxide sintered body of the present invention, asdescribed above, it is necessary that relation between the In₂O₃ phaseof a bixbyite-type structure as the main phase, where cerium seldommakes a solid solution, and the CeO₂ phase of a fluorite-type structure,as a second phase is expressed by an X-ray diffraction peak intensityratio (I), defined by the following formula (1), and said X-raydiffraction peak intensity ratio is equal to or lower than 25%. Inparticular, it is preferable that the X-ray diffraction peak intensityratio is equal to or lower than 20%. The X-ray diffraction peakintensity ratio over 25% generates arching frequently in sputtering, andis thus not preferable.I=[CeO₂ phase (111)/In₂O₃ phase (222)]×100[%]  (1)

It is necessary that the CeO₂ phase of a fluorite-type structure, as asecond phase, is finely dispersed as crystal grains having an averageparticle diameter of equal to or smaller than 3 μm, and the averageparticle diameter of the crystal grain over 3 μm generates arcingfrequently in sputtering, and is thus not preferable. It is morepreferable that the average particle diameter of the crystal grain isequal to or smaller than 2 μm.

(c) A Sintered Body Texture and a Nodule

The oxide sintered body of the present invention has a sintered bodytexture which little generates a nodule in direct-current sputtering.

In the case where the oxide sintered body containing indium and ceriumas oxides is processed, for example, as a target for direct-currentsputtering, crystal grains of the In₂O₃ phase of a main phase and theCeO₂ phase as the second phase are present at said target surface, andthere may be a case causing a problem of nodule generation in the targetsurface, depending on the crystal particle diameter or dispersing stateof CeO₂ phase among them. The CeO₂ phase has such characteristics aselectric resistance is higher as compare with the In₂O₃ phase, and islittle sputtered. A general oxide sintered body of ITO is composed ofcrystal grains of a coarse In₂O₃ phase with an average particle diameterof about 10 μm, where Sn makes a solid solution, however, in the casewhere the oxide sintered body containing indium and cerium as oxideswithin the above composition range is composed of coarse crystal grainsin both of the In₂O₃ phase and the CeO₂ phase, similarly as the ITOsintered body, the crystal grains of the In₂O₃ phase are sputteredpreferentially, but sputtering of the crystal grains of the CeO₂ phasedoes not proceed, and thus coarse crystal grains of the CeO₂ phaseremain at the target surface as a digging residue, resulting in gradualgrowth of the nodule starting from this digging residue, and frequentoccurrence of abnormal discharge such as arcing or the like.

In order to suppress the nodule formed by the digging residue in thisway, it is necessary to make a finer texture of the oxide sintered bodycontaining indium and cerium, as an oxide, within the above compositionrange. That is, it is necessary to finely disperse the crystal grain ofthe CeO₂ phase in said oxide sintered body. Because the CeO₂ phase hasconductivity in a reduced state, the CeO₂ phase itself never becomes acause of abnormal discharge and is unlikely to become a starting pointof nodule growth, due to being finely dispersed.

In FIG. 1, there are shown a secondary electron image by a scanningelectron microscope (SEM), and surface analysis result by an energydispersive X-ray analysis method (EDS) of the cross-section of the oxidesintered body containing cerium in a content of 9% by atom, as anatomicity ratio of Ce/(In+Ce), as a reference example of the In₂O₃phase, as a main phase, finely dispersed with the crystal grain of theCeO₂ phase. Although not distinguishable in a secondary electron imageat the upper left of the photo, in the surface analysis result of thelower right photo, the In₂O₃ phase as the main phase, and the CeO₂ phaseas the second phase are clearly distinguished. This is considered thatcerium little makes a solid solution in the In₂O₃ phase of a bixbyitestructure, or indium little makes a solid solution also in the CeO₂phase of a fluorite-type structure, which is a dispersed phase. Here, ithas been confirmed that, in the crystal grain of the CeO₂ phase, thereare many particles with an average particle diameter of equal to orsmaller than 3 μm, particularly equal to or smaller than 1 μm, and useof a target obtained by processing of this oxide sintered body littlegenerates a nodule from a digging residue as a starting point insputtering.

In this way, as shown in FIG. 1, it is clear that a texture having theIn₂O₃ phase as a main crystal phase, and the CeO₂ phase finely dispersedas a second phase, is effective in suppressing a nodule, which tends tobe generated accompanying with progress of sputtering.

In addition, in FIG. 5, there are shown a secondary electron image by ascanning electron microscope (SEM) , and surface analysis result by anenergy dispersive X-ray analysis method (EDS) of the cross-section ofthe oxide sintered body of Example 3 having a cerium content of 4% byatom, as an atomicity ratio of Ce/(In+Ce), and a titanium content of 1%by atom, as an atomicity ratio of Ti/(In+Ce+Ti), as an example ofcrystal grains of the CeO₂ phase finely dispersed in the In₂O₃ phase ofa main crystal phase. Although not distinguishable in a secondaryelectron image at the upper left of the photo, in the surface analysisresult of the lower right photo, the In₂O₃ phase of the main phase, andthe CeO₂ phase of the second phase are clearly distinguished. The reasonis considered that cerium little makes a solid solution in the In₂O₃phase of a bixbyite-type structure, or indium little makes a solidsolution also in the CeO₂ phase of a fluorite-type structure, which is adispersed phase. In addition, because an aspect of a co-presence stateof indium and titanium in a part of the crystal grains is observed fromthe surface analysis result at the lower right photo, it is judged thatTi has a solid solution in the In₂O₃ phase of a main phase. Here, thecrystal grain of the CeO₂ phase has many particles with an averageparticle diameter of equal to or smaller than 3 μm, and it has beenconfirmed that use of a target obtained by processing of this oxidesintered body little generates a nodule starting from a digging residuein sputtering. In this way, as shown in FIG. 5, it is clear that thetexture having the In₂O₃ phase as a main crystal phase, finely dispersedwith the CeO₂ phase as a second phase, is effective to suppress a nodulewhich tends to be generated accompanying with proceeding of sputtering.

As described above, in order to suppress a nodule, it is necessary thatthe average particle diameter of crystal grains composed of the CeO₂phase is equal to or smaller than 3 μm, and still more it is preferableto be controlled at equal to or smaller than 2 μm. It should be notedthat, in the case where the cerium content in the oxide sintered body isbelow 0.3% by atom, crystal grains of a fine CeO₂ phase become not to bedispersed uniformly, and the nodule suppression method of the presentinvention becomes not effective.

In this way, in the present invention, a dispersed state of the CeO₂phase in the oxide sintered body is specified, as well as a compositionratio to the In₂O₃ phase is specified. The composition ratio of theIn₂O₃ phase of a main crystal phase and the CeO₂ phase of a dispersedphase, in the oxide sintered body of the present invention, has theX-ray diffraction peak intensity ratio (I), defined by the above formula(1), of equal to or lower than 25%.

In addition, in the present invention, strength is enhanced by makingfiner crystal grains composing the oxide sintered body. That is, theoxide sintered body becomes the one difficult to fracture, even inreceiving impact by heat or the like, by increasing power to be chargedin sputtering.

It should be noted that any of at least one or more kinds of the M metalelement selected from the metal element group consisting of titanium,zirconium, hafnium, molybdenum and tungsten preferentially makes a solidsolution in the In₂O₃ phase, however, there may also the case where itmakes a solid solution also in the CeO₂ phase, when atomic ratiorelative to total metal elements is over 1% by atom. Because the CeO₂phase, where the M element made a solid solution, decreasesconductivity, there may be the case where the CeO₂ phase itself becomesa cause of arcing in direct-current sputtering, or becomes a cause ofarcing by generating a nodule as a digging residue, and is thus notpreferable.

In the oxide sintered body of the present invention, most preferable oneis the one where titanium only is selected in the M metal element group.That is, in the oxide sintered body containing, as an oxide, indium,cerium and titanium, such one is preferable that has the cerium contentof 0.3 to 9% by atom, as an atomicity ratio of Ce/(In+Ce+Ti), thetitanium content of equal to or lower than 1% by atom, as an atomicityratio of Ti/(In+Ce+Ti), and the total content of cerium and titanium ofequal to or lower than 9% by atom, as an atomicity ratio of(Ce+Ti)/(In+Ce+Ti)), where the In₂O₃ phase of a bixbyite-type structureis a main crystal phase, and the CeO₂ phase of a fluorite-typestructure, as a second phase, and an oxide phase of the M element arefinely dispersed, as crystal grains having an average particle diameterof equal to or smaller than 3 μm.

As described above, the case of the addition of only cerium to theindium oxide-type transparent conductive film does not necessarilygenerate carrier electrons stably. Therefore, in order to stablygenerate carrier electrons, it is effective to add both cerium andtitanium, not adding only cerium. In addition, in such applicationswhere low specific resistance has priority than high refractive index,it is preferable to generate relatively more carrier electrons in thecrystalline transparent conductive film. In this case also, the additionof both cerium and the titanium is more effective than the addition ofonly cerium. Titanium has generation effect of carrier electrons severaltimes high, as compared with cerium, and required amount of carrierelectrons can be generated by only a trance amount of the addition.Because it is necessary to decrease the addition amount of cerium tocompensate the addition of titanium, specific resistance can bedecreased effectively, although refractive index decreases a little.

It should be noted that, as described above, because tin has far highergeneration effect of carrier electrons, as compared with titanium, tinshould not be contained. It is not preferable to contain also elementssuch as silicon, germanium, antimony, bismuth and tellurium and thelike, by the same reason, although the above effect thereof is a littleinferior, as compared with tin.

From the above reason, it is preferable that the cerium content is 0.3to 9% by atom, as an atomicity ratio of Ce/(In+Ce+Ti), the Ti content isequal to or lower than 1% by atom, as an atomicity ratio ofTi/(In+Ce+Ti), and the total content of cerium and titanium is equal toor lower than 9% by atom, as an atomicity ratio of (Ce+Ti)/(In+Ce+Ti).

The Ti content over 1% by atom, as an atomicity ratio of Ti/(In+Ce+Ti),provides too high carrier electron concentration in the crystallinetransparent conductive film, causing decrease in refractive index, andis thus not preferable rather. Still more, in the oxide sintered body,titanium preferentially makes a solid solution in the In₂O₃ phase,however, there may also be the case where it makes a solid solution inthe CeO₂ phase, when the amount is over 1% by atom. The CeO₂ phasedecreases conductivity, even in a reduced state, when titanium makes asolid solution, causing arcing. In addition, when total content ofcerium and titanium is over 9% by atom, as an atomicity ratio of(Ce+Ti)/(In+Ce+Ti), because refractive index decreases similarly, mainlycaused by increase in titanium content, and is thus not preferable.

2. The Production Method for the Oxide Sintered Body

In the production method for the oxide sintered body of the presentinvention, raw material powder containing indium oxide powder and ceriumoxide powder is mixed, or further oxide powder of at least one or morekinds of the metal element selected from the M metal element groupconsisting of titanium, zirconium, hafnium, molybdenum and tungsten,preferably titanium oxide powder, is added and mixed, then the mixedpowder is molded, and the molding is sintered by a normal pressuresintering method. Alternatively, the above mixed powder is molded by ahot press method and sintered.

The average particle diameter of the above raw material powder is set atequal to or smaller than 1.5 μm, and the oxide sintered body aftersintering is subjected to heat treatment at temperature and for timesufficient to obtain the oxide sintered body, where the In₂O₃ phase of abixbyite-type structure is a main crystal phase, and the CeO₂ phase of afluorite-type structure is finely dispersed, as a second phase, ascrystal grains having an average particle diameter of equal to orsmaller than 3 μm. In this way, the oxide sintered body where the In₂O₃phase of a bixbyite-type structure is a main crystal phase, and the CeO₂phase of a fluorite-type structure is finely dispersed, as a secondphase, as crystal grains having an average particle diameter of equal toor smaller than 3 μm, more preferably equal to or smaller than 2 μm, canbe obtained.

That is, performance of the oxide sintered body, having the above phasecomposition and a composition of each phase, largely depends onproduction condition of the oxide sintered body, for example, particlediameter of raw material powder, mixing condition and firing condition.

The oxide sintered body of the present invention requires that theindium oxide powder and the cerium oxide powder adjusted to have anaverage particle diameter of equal to or smaller than 1.5 μm are used,as raw material powder, as well as oxide powder of at least one or morekinds of the M element selected from the M metal element groupconsisting of titanium, zirconium, hafnium, molybdenum and tungsten,particularly titanium oxide powder is used as raw material powder.

As described above, by setting the average particle diameter of rawmaterial powder at equal to or smaller than 1.5 μm, it is possible toattain a texture of the oxide sintered body of the present invention,which has the In₂O₃ phase of a bixbyite-type structure, as a main phase,where the second phase composed of the CeO₂ phase of a fluorite-typestructure is present, however, crystal grains composed of the CeO₂ phaseare finely and uniformly dispersed relative to the main phase, and havean average particle diameter of equal to or smaller than 3 μm. Stillmore, by adjusting indium oxide powder and cerium oxide powder so as tohave an average particle diameter of equal to or smaller than 1 μm, itis possible to control average particle diameter of the crystal graincomposed of the second CeO₂ phase to equal to or smaller than 2 μm.

When the indium oxide powder or cerium oxide powder and titanium oxidepowder with the average particle diameter over 1.5 μm is used as rawmaterial powder, the average particle diameter of the crystal grainscomposed of the CeO₂ phase, which is present in the resultant oxidesintered body, along with the In₂O₃ phase as a main phase, becomes over3 μm.

In NON-PATENT LITERATURE 2, there has been explained, as for sinteringmechanism of ITO, that by increasing heating temperature raising speedof an ITO molding more than certain speed in sintering, time forgeneration of neck growth and particle growth, byevaporation·condensation mechanism or surface diffusion mechanism, wheremaking a finer texture little progresses, can be shortened, and atemperature region of volume diffusion can be reached in a state thatdriving force of sintering is still maintained, therefore making a finertexture is progressed and sintering density is enhanced. In this case,inter-particle distance “d” before sintering, which corresponds toparticle diameter of raw material powder, contracts to “d′”, by masstransfer caused by volume diffusion during a sintering process. In thisway, when limited to sintering of two particles of raw material powder,diameter of the crystal grain of the sintered body becomes “2d′”.However, usually, because a plurality of particles of the same kinds ofthe oxides are adjacent, it is considered that diameter of the crystalgrain of the sintered body is over “2d′”, finally.

In the case where cerium little makes a solid solution in indium oxide,as in the present invention, it is important to decrease particlediameter of cerium oxide raw material powder, to decrease crystal graindiameter of the cerium oxide phase of the sintered body.

As described above, large crystal grains of the CeO₂ phase with theaverage particle diameter over 3 μm tend not to be sputtered and tobecome a digging residue. Therefore, in the case of continuedsputtering, it makes a comparative large residue on the surface oftarget, and it makes the origin of nodule to cause the abnormaldischarge such as arcing.

Indium oxide powder is a raw material of ITO (indium-tin oxide), anddevelopment of fine indium oxide powder, having excellent sinteringproperty, has been promoted with improvement of ITO. The raw materialpowder, with an average particle diameter of equal to or smaller than1.5 μm, more preferably equal to or smaller than 1 μm, is easilyavailable, due to use in a large quantity also at present, as a rawmaterial of ITO.

However, in the case of cerium oxide powder, powder with an averageparticle diameter of equal to or smaller than 1.5 μm, more preferablyequal to or smaller than 1 μm, suitable as raw material powder forproducing the sintered body, in a state utilizable as it is withoutperforming crushing or the like, is not easily available, due to smalleruse quantity as compared with indium oxide powder. Therefore, the coarsecerium oxide powder is required to be crushed to an average particlediameter of equal to or smaller than 1.5 μm, more preferably equal to orsmaller than 1 μm.

In addition, also in the case of oxide powder of at least one or morekinds of an metal element selected from the metal element group composedof titanium, zirconium, hafnium, molybdenum and tungsten, to be addedthereto, similarly as in the cerium oxide powder, it is difficult toobtain raw material powder with an average particle diameter of 1.5 μm,more preferably equal to or smaller than 1 μm, therefore it is requiredto crushed coarse oxide powder to an average particle diameter of 1.5μm, more preferably equal to or smaller than 1 μm.

In order to obtain the oxide sintered body of the present invention,after mixing of raw material powder containing indium oxide powder andcerium oxide powder having the above average particle diameter, themixed powder is molded and the molding is sintered by a normal pressuresintering method, or the mixed powders are molded and sintered by a hotpress method. The normal pressure sintering method is a simple andconvenient, and industrially advantageous method, and thus a preferablemethod, however, a hot press method may be used as well, if necessary.

1) The Normal Pressure Sintering Method

In the case where the normal pressure sintering method is used to obtainthe oxide sintered body, a molding is prepared first. The above rawmaterial powder is charged into a resin pot for mixing along with abinder (for example, PVA is used) or the like, by use of a wet-type ballmill or the like. In order to obtain the oxide sintered body, it ispreferable that the above ball mill mixing is performed for 18 hours orlonger. In this case, as a ball for mixing, a hard-type ZrO₂ ball may beused. After the mixing, slurry is taken out for performing offiltration, drying and granulation. After that, the resultant granulatedsubstance is molded, under a pressure of from about 9.8 MPa (0.1ton/cm²) to 294 MPa (3 ton/cm²), by use of a cold isostatic press toobtain a molding.

In a sintering step of the normal pressure sintering method, heating isperformed at a predetermined temperature range under atmosphere ofoxygen presence. Sintering is performed at 1250 to 1650° C., morepreferably at 1300 to 1500° C., under atmosphere where oxygen gas isintroduced into air inside a sintering furnace. Sintering time ispreferably from 10 to 30 hours, more preferably from 15 to 25 hours.

By use of the indium oxide powder, cerium oxide powder and oxide powderof the M element such as titanium oxide, which is adjusted to have theabove average particle diameter of equal to or smaller than 1.5 μm orsmaller, more preferably equal to or smaller than 1 μm, as raw materialpowder, and at the sintering temperature of the above range, it ispossible to obtain a dense oxide sintered body, where the crystal grainsmade of the CeO₂ phase, having an average particle diameter of equal toor smaller than 3 μm, more preferably equal to or smaller than 2 μm, arefinely dispersed in the In₂O₃ phase matrix.

The too low sintering temperature does not progress a sintering reactionsufficiently. In particular, in order to obtain the oxide sintered bodywith a density of equal to or higher than 6.0 g/cm³, the temperature ispreferably equal to or higher than 1250° C. On the other hand, thesintering temperature over 1650° C. significantly increases growth ofthe crystal grains of the CeO₂ phase in the oxide sintered body. Thistoo large crystal grain of the CeO₂ phase becomes a cause of arcing.

In PATENT LITERATURE 3, similarly as in PATENT LITERATUREs 1 an 2,because quite a large quantity of titanium or tin is added, in additionto indium and cerium, in a conventional technology, cerium makes a solidsolution in the indium oxide phase, however, the present invention ischaracterized in that, because titanium addition amount is low, and tinis not contained, cerium does not make a solid solution in the indiumoxide phase.

Sintering atmosphere is preferably atmosphere in the presence of oxygen,and still more preferably atmosphere where oxygen gas is introduced intoair inside the sintering furnace. Presence of oxygen in sinteringenables to make higher density of the oxide sintered body. Intemperature increase up to sintering temperature, in order to preventcracking of a sintered body and progress de-binder, it is preferable toset temperature increasing rate in a range of from 0.2 to 5° C./min. Inaddition, as needed, different temperature increasing rates maybecombined to raise temperature up to sintering temperature.

In the step for increasing temperature, specific temperature may be heldfor a certain period aiming at progressing of de-binder or sintering. Incooling after sintering, it is preferable to stop introduction ofoxygen, and lower temperature down to 1000° C. at temperature decreasingrate in a range of from 0.2 to 5° C./min, in particular, 0.2° C./min to1° C./min.

2) The Hot Press Method

In the present invention, in the case where the hot press method isadopted in producing the oxide sintered body, the mixed powder is moldedand sintered at 700 to 950° C. for 1 to 10 hours under a pressure of2.45 to 29.40 MPa under inert gas atmosphere or in vacuum. The hot pressmethod is capable of decreasing oxygen content in the sintered body, dueto subjecting raw material powder of the oxide sintered body to moldingand sintering under reducing atmosphere, as compared with the abovenormal pressure sintering method. However, caution is required inmolding and sintering at a high temperature over 950° C., because ofreduction of indium oxide and melting as metal indium.

Next, one example of production condition in the case of obtaining theoxide sintered body of the present invention by the hot press method isshown. That is, firstly, indium oxide powder with an average particlediameter of equal to or smaller than 1.5 μm, more preferably equal to orsmaller than 1 μm, along with cerium oxide powder with an averageparticle diameter of equal to or smaller than 1.5 μm, more preferablyequal to or smaller than 1 μm, still more oxide powder of at least oneor more kinds of the metal element selected from the metal element groupconsisting of titanium, zirconium, hafnium, molybdenum and tungsten,with an average particle diameter of equal to or smaller than 1.5 μm,more preferably equal to or smaller than 1 μm are prepared as rawmaterial powder, so as to attain predetermined ratio.

The prepared raw material powder is sufficiently mixed similarly as inball mill mixing of a normal pressure sintering method, preferably for amixing time of 18 hours or longer. Then the granulated mixed powder issupplied into a carbon container to be subjected to sintering by the hotpress method. Sintering temperature may be set at from 700 to 950° C.,pressure may be set at from 2.45 MPa to 29.40 MPa (25 to 300 kgf/cm²),and sintering time may be set from about 1 to 10 hours. Atmosphereduring hot press is preferably under inert gas such as Ar, or in vacuum.

In the case of obtaining a target for sputtering, more preferably,sintering temperature maybe set at from 800 to 900° C., pressure may beat from 9.80 MPa to 29.40 MPa (100 to 300 kgf/cm²), and sintering timemay be from 1 to 3 hours.

3. The Target for Sputtering

The target for sputtering is obtained by cutting the oxide sintered bodyof the present invention to a predetermined size, and polishingprocessing of the surface to adhere to a backing plate.

It is required that the target for sputtering is controlled to have adensity of equal to or higher than 6.3 g/cm³, preferably equal to orhigher than 6.8 g/cm³, and particularly preferably equal to or higherthan 7.0 g/cm³. The density below 6.3 g/cm³ causes cracks or fracturesand nodule generation.

The density below 6.3 g/cm³ provides inferior strength of the sinteredbody itself, and thus cracks or fractures easily generate even for smalllocal thermal expansion.

4. The Transparent Conductive Film Containing Indium and Cerium, Alongwith a Film-Formation Method Thereof

In the present invention, the mainly crystalline transparent conductivefilm is formed on a substrate, using the above oxide sintered body asthe target for sputtering.

As the substrate, various plates or films may be used, such as glass,synthetic quartz, a synthetic resin such as PET or polyimide, astainless steel plate and the like, in response to applications. Inparticular, because heating is required in forming the crystallinetransparent conductive film, the substrate having heat resistance isnecessary.

In the sputtering method, increase in direct-current power to be chargedhas been performed generally to enhance film-formation rate of thetransparent conductive film. As described above, in the oxide sinteredbodies of the present invention, the In₂O₃ phase of a bixbyite-typestructure is a main crystal phase, and the crystal grains of the CeO₂phase as a second phase are uniformly and finely dispersed, having anaverage particle diameter of equal to or smaller than 3 μm, and morepreferably equal to or smaller than 2 μm, which little provides astarting point of nodule growth. Therefore, even when direct-currentpower to be charged is increased, nodule generation is suppressed andthus abnormal discharge such as arcing or the like can be suppressed.

1) Film-formation by the Sputtering Method

In the case of forming the transparent conductive film on a substrate bythe sputtering method, a target for sputtering obtained by fabricatingthe oxide sintered body with a density of equal to or higher than 6.3g/cm³ is used. As a sputtering method, there may be used a highfrequency sputtering method (it may be referred to as an RF sputteringmethod), or a pulse sputtering method, however, in particular, accordingto a direct-current sputtering method (it may be referred to as a DCsputtering method), thermal influence in film-formation is small, andhigh rate film-formation is possible, and is thus industriallyadvantageous. It should be noted that the pulse sputtering method is amethod for adopting a frequency of several hundred kHz, which is lowerthan a general frequency of 13.56 MHz in the high frequency sputteringmethod, or changing waveform of applied current and applied voltage (forexample, change to a rectangular form). In order to form the transparentconductive film by the direct-current sputtering method, it ispreferable to use mixed gas composed of inert gas and oxygen, inparticular, argon and oxygen, as sputtering gas. In addition, it ispreferable to perform sputtering by setting pressure inside a sputteringapparatus at 0.1 to 1 Pa, in particular, 0.2 to 0.8 Pa.

In the present invention, pre-sputtering may be performed, by generatingdirect-current plasma, for example, by vacuum exhaustion to equal to orlower than 2×10⁻⁴Pa, then introducing mixed gas composed of argon andoxygen to set gas pressure at 0.2 to 0.5 Pa, and applying direct-currentpower so that direct-current power relative to target area, that is,direct-current power density becomes in a range of about 1 to 3 W/cm².It is preferable that, after performing this pre-sputtering for 5 to 30minutes, sputtering is performed by correcting a substrate position, asneeded.

In the present invention, film-formation is possible at room temperaturewithout heating of the substrate, however, the substrate may also beheated at from 50 to 500° C., in particular, from 250 to 500° C. Forexample, in the blue LED requiring a highly precise transparentelectrode, in order to make lower resistance by once forming anamorphous transparent conductive film, and after performing patterningby wet etching using a weak acid, and by crystallization by heattreatment under non-oxidative atmosphere, it is better for the substratein film-formation to be maintained at low temperature such as at thevicinity of room temperature. Other than the above, in a solar cell,because patterning by wet etching using a weak acid is not necessary,the crystalline transparent conductive film is formed by maintaining thesubstrate temperature at a high temperature of equal to or higher than250° C. In addition, depending on applications, because the one with lowmelting point, such as a resin plate, a resin film is used, as thesubstrate, it is desirable, in this case, to perform film-formationwithout heating.

2) The Transparent Conductive Film Obtained

In this way, by using the target for sputtering prepared from the oxidesintered body of the present invention, an amorphous or crystallinetransparent conductive film superior in optical characteristics andconductivity can be produced on a substrate in relatively highfilm-formation rate by the direct-current sputtering method.

Composition of the resultant transparent conductive film becomes nearlyequal to that of the target for sputtering. Film thickness is differentdepending on an application, however, 10 to 1000 nm may be attained. Itshould be noted that the amorphous transparent conductive film can beconverted to a crystalline one by heating it at 300 to 500° C. for 10 to60 minutes under inert gas atmosphere.

Specific resistance of the crystalline transparent conductive film wascalculated from a product of surface resistance measured by a four-probemethod using a resistivity meter, and film thickness, and is equal to orlower than 8×10⁻⁴ Ω·cm. It should be noted that even when beingamorphous, it is well possible that the specific resistance shows equalto or lower than 8×10⁻⁴Ω·cm. Carrier electron concentration and mobilitythereof of the crystalline transparent conductive film are determined byhole effect measurement and the latter is equal to or higher than 35cm²V⁻¹s⁻¹. A generated phase of this film is identified by X-raydiffraction measurement, and found to be only the indium oxide phase,different from the oxide sintered body. In addition, refractive index ismeasured using a spectro-elipsometer, and is equal to or higher than 2.1at a wavelength of 460 nm.

It should be noted that the crystalline or amorphous transparentconductive film formed by the oxide sintered body of the presentinvention is suitable for also applications not requiring low specificresistance and requiring only high refractive index, for example, anoptical disk application and the like.

EXAMPLES

Explanation will be given below specifically on the present inventionwith reference to Examples and Comparative Examples, however, thepresent invention should not be limited thereto.

(Evaluation of the Oxide Sintered Body)

By use of a mill end, density of the oxide sintered body obtained wasdetermined by the Archimedes' method. Subsequently a part of the millend was crushed to perform identification of generated phases of theresultant oxide sintered body by a powder method, with an X-raydiffraction apparatus (X′pert PRO MPD, manufactured by Philips Co.,Ltd.). Then, X-ray diffraction peak intensity ratio (I), defined by thefollowing formula, was determined:I=[CeO₂ phase (111)/In₂O₃ phase (222)]×100[%]  (1)

In addition, by using a part of the powder, composition analysis of theoxide sintered body was performed by an ICP emission spectroscopy. Stillmore, with a scanning electron microscope, and an energy dispersiveX-ray analysis method (SEM-EDS, ULTRA55, manufactured by Carl ZeissJapan Co., Ltd., and QuanTax QX400, manufactured by Bulker Japan Cp.,Ltd.), texture observation of the oxide sintered body, along withsurface analysis were performed. From the image analysis result of theseimages, average particle diameter of the crystal grains composed of theCeO₂ phase was determined.

(Evaluation of Fundamental Characteristics of the Transparent ConductiveFilm)

Composition of the resultant transparent conductive film was studied byan ICP emission spectroscopy. Film thickness of the transparentconductive film was measured with a surface roughness tester (Alpha-StepIQ, manufactured by Tencor Japan Corp.). Film-formation rate wascalculated from film thickness and film-formation time. Specificresistance of the film was calculated from a product of surfaceresistance measured by a four-probe method using a resistivity meter(Loresta EP MCP-T360 model, manufactured by DIA Instruments Co., Ltd.),and film thickness. Carrier electron concentration of the film andmobility thereof were determined by hole effect measurement. A generatedphase of the film was identified by X-ray diffraction measurement,similarly as in the oxide sintered body. In addition, refractive indexwas measured using a spectro-elipsometer (VASE, manufactured by J. A.Woolam Co., Ltd.) , and to evaluate characteristics for, in particular,blue light, refractive index of a wavelength of 460 nm was compared.

Reference Example 1

Zinc oxide powder and cerium oxide powder were adjusted to have anaverage particle diameter of equal to or smaller than 1 μm to prepareraw material powder. The powder were prepared, so that cerium content is9% by atom, as atom number ratio represented by Ce/(In+Ce), and chargedin a pot made of a resin, together with water to mix in a wet-type ballmill. In this case, hard-type ZrO₂ balls were used, and mixing time wasset to 18 hours. After the mixing, slurry was taken out, filtered, driedand granulated. The granulated substance was converted to a moldingunder a pressure of 3 tons/cm², using a cold isostatic press.

Then, the molding was sintered as follows. Sintering was performed underatmosphere by introducing oxygen into air inside a sintering furnace ina rate of 5 L/minute per 0.1 m³ of furnace volume, at a sinteringtemperature of 1400° C. for 20 hours. In this case, temperatureincreasing rate was 1° C./minute, and in cooling after sintering, oxygenintroduction was stopped, and temperature was cooled to 1000° C., at arate of 10° C./minute.

The resultant oxide sintered body was processed to a size of 152 mm indiameter and 5 mm in thickness, and the sputtering surface thereof waspolished using a cup grinding stone so that maximal height, Rz, becomesequal to or lower than 3.0 μm. The processed oxide sintered body wasbond to a backing plate made of oxygen-free copper using metal indium,to prepare a sputtering target.

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next, asshown in FIG. 2, phase identification of the oxide sintered body wasperformed by X-ray diffraction measurement. From FIG. 2, it wasconfirmed to be composed of the In₂O₃ phase with a bixbyite-typestructure, and the CeO₂ phase with a fluorite-type structure. X-raydiffraction peak intensity ratio of the CeO₂ phase (111), represented bythe above equation (1), was 16%.

Density of the oxide sintered body was measured and found to be 6.87g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM (refer to the above FIG. 1), and found that averageparticle diameter of the CeO₂ phase was 1.1 μm. These results are shownin Table 1.

Next, the sputtering target was attached to a cathode for a non-magneticsubstance target of a direct-current magnetron sputtering apparatus(SPF-530H, manufactured by ANELVA Corp.) equipped with a direct-currentpower source not having arc-discharge suppression function. Synthesisquartz, with a size of 50 mm in side length and 0.5 mm in thickness, wasused as a substrate, and distance between the target and the substratewas fixed to 49 mm. Mixed gas of argon and oxygen was introduced, sothat ratio of oxygen was 1.0%, after vacuum exhausting to below 1×10⁻⁴Pa, to adjust gas pressure to 0.3 Pa. It should be noted that in theabove ratio of oxygen of 1.0%, specific resistance exhibited the lowestvalue.

A direct-current power of 200 W (1.10 W/cm²) was applied to generatedirect-current plasma to perform sputtering. The direct-currentsputtering was continued till attaining a cumulative charge power valueof 12.8 KWh, which is calculated from a product of direct-current powercharged and sputtering time. Arcing did not generate during this period,and discharge was stable. After completion of the sputtering, the targetsurface was observed and found no particular nodule generation. Then bychanging direct-current power to 200, 400, 500 and 600 W (1.10 to 3.29W/cm²), sputtering was performed for 10 minutes under each power tomeasure arcing occurrence number of times. Under any power, arcing didnot generate, and average arcing occurrence number of times per minuteunder each direct-current power was zero.

Subsequently, film-formation was performed by direct-current sputtering.After pre-sputtering for 10 minutes, the substrate was arranged justover the sputtering target, that is, at a stationary opposed position,and sputtering was performed at a substrate temperature of 500° C. toform a transparent conductive film with a film thickness of 200 nm. Itwas confirmed that the composition of the resultant transparentconductive film was nearly the same as that of the target.

By measurement of specific resistance of the film, it was found to be6.6×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 2.6×10²⁰ cm⁻³, and carrierelectron mobility was 36 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.21. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Reference Example 2

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder, adjusted to have an average particle diameter of equal to orsmaller than 1.5 μm, was prepared, so that cerium content became 7% byatom, as atom number ratio represented by Ce/(In+Ce).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃ phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111) , represented by the above equation (1), was 14%.

Density of the oxide sintered body was measured and found to be 6.88g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 2.7 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 500° C. to forma transparent conductive film witha film thickness of 200 nm. It was confirmed that the composition of theresultant transparent conductive film was nearly the same as that of thetarget.

By measurement of specific resistance of the film, it was found to be5.4×10⁻⁴Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 2.5×10²⁰ cm⁻³, and carrierelectron mobility was 46 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.20. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Reference Example 3

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder, adjusted to have an average particle diameter of equal to orsmaller than 1 μm, was prepared, so that cerium content became 5% byatom, as atom number ratio represented by Ce/(In+Ce).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃ phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111), represented by the above equation (1), was 9%.

Density of the oxide sintered body was measured and found to be 6.92g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 1.3 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 400° C. to forma transparent conductive film witha film thickness of 200 nm. It was confirmed that the composition of theresultant transparent conductive film was nearly the same as that of thetarget.

By measurement of specific resistance of the film, it was found to be4.6×10⁻⁴Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 2.4×10²⁰ cm⁻³, and carrierelectron mobility was 57 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.19. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Next, substrate temperature was set at room temperature (25° C.) toperform film-formation by a direct-current sputtering, and then heattreatment was performed under nitrogen.

By measurement of specific resistance of the film formed at roomtemperature, it was found to be 7.5'10⁻⁴ Ω·cm. In addition, measurementof hole effect was performed and found that carrier electronconcentration was 4.9×10²⁰ cm⁻³, and carrier electron mobility was 17cm²V⁻¹s⁻¹. Refractive index of a wavelength of 460 nm was 2.17.Crystallinity of the film was identified by X-ray diffractionmeasurement, and confirmed to be to be an amorphous film.

Subsequently, heat treatment of this amorphous film was performed at400° C. for 30 minutes under nitrogen atmosphere. As a result, specificresistance of the film was found to be 4.9×10⁻⁴ Ω·cm. In addition,measurement of hole effect was performed and found that carrier electronconcentration was 2.2×10²⁰ cm⁻³, and carrier electron mobility was 58cm²V⁻¹s⁻¹. Refractive index of a wavelength of 460 nm was 2.20.Crystallinity of the film was identified by X-ray diffractionmeasurement, and confirmed to be to be a crystalline film composed of anindium oxide phase only, and cerium to be in a solid solution state inthe indium oxide phase.

Reference Example 4

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder, adjusted to have an average particle diameter of equal to orsmaller than 1.5 μm, was prepared, so that cerium content became 4% byatom, as atom number ratio represented by Ce/(In+Ce).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃ phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111), represented by the above equation (1), was 8%.

Density of the oxide sintered body was measured and found to be 6.91g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 2.8 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 400° C. to forma transparent conductive film witha film thickness of 200 nm. It was confirmed that the composition of theresultant transparent conductive film was nearly the same as that of thetarget.

By measurement of specific resistance of the film, it was found to be4.2×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 2.3×10²⁰ cm⁻³, and carrierelectron mobility was 65 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.17. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Reference Example 5

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder, adjusted to have an average particle diameter of equal to orsmaller than 1 μm, was prepared, so that cerium content became 1% byatom, as atom number ratio represented by Ce/(In+Ce).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃ phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111), represented by the above equation (1), was 2%.

Density of the oxide sintered body was measured and found to be 6.86g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 1.1 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 400° C. to form a transparent conductive filmwith a film thickness of 200 nm. It was confirmed that the compositionof the resultant transparent conductive film was nearly the same as thatof the target.

By measurement of specific resistance of the film, it was found to be4.4×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 1.6×10²⁰ cm⁻³, and carrierelectron mobility was 88 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.14. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Reference Example 6

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder, adjusted to have an average particle diameter of equal to orsmaller than 1 μm, was prepared, so that cerium content became 0.3% byatom, as atom number ratio represented by Ce/(In+Ce).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111), represented by the above equation (1), was 0.5%.

Density of the oxide sintered body was measured and found to be 6.70g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 1.2 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 300° C. to forma transparent conductive film witha film thickness of 200 nm. It was confirmed that the composition of theresultant transparent conductive film was nearly the same as that of thetarget.

By measurement of specific resistance of the film, it was found to be7.6×10⁻⁴Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 1.0×10²⁰ cm⁻³, and carrierelectron mobility was 82 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.13. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Example 1

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder was obtained, by adjusting indium oxide powder, cerium oxidepowder and titanium oxide powder to have an average particle diameter ofequal to or smaller than 1.5 μm, so that cerium content became 8% byatom, as atom number ratio represented by Ce/(In+Ce+Ti), and titaniumcontent became 1% by atom, as atom number ratio represented byTi/(In+Ce+Ti).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃ phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111), represented by the above equation (1), was 25%.

Density of the oxide sintered body was measured and found to be 7.06g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 2.7 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 400° C. to form a transparent conductive filmwith a film thickness of 200 nm. It was confirmed that the compositionof the resultant transparent conductive film was nearly the same as thatof the target.

By measurement of specific resistance of the film, it was found to be5.6×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 3.1×10²⁰ cm⁻³, and carrierelectron mobility was 36 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.14. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Example 2

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder was obtained, by adjusting indium oxide powder, cerium oxidepowder and titanium oxide powder to have an average particle diameter ofequal to or smaller than 1 μm, so that cerium content became 5% by atom,as atom number ratio represented by Ce/(In+Ce+Ti), and titanium contentbecame 0.5% by atom, as atom number ratio represented by Ti/(In+Ce+Ti).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃ phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111), represented by the above equation (1), was 14%.

Density of the oxide sintered body was measured and found to be 7.01g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 1.5 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 400° C. to forma transparent conductive film witha film thickness of 200 nm. It was confirmed that the composition of theresultant transparent conductive film was nearly the same as that of thetarget.

By measurement of specific resistance of the film, it was found to be5.4×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 2.5×10²⁰ cm⁻³, and carrierelectron mobility was 46 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.17. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Example 3

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder was obtained, by adjusting indium oxide powder, cerium oxidepowder and titanium oxide powder to have an average particle diameter ofequal to or smaller than 1 μm, so that cerium content became 4% by atom,as atom number ratio represented by Ce/(In+Ce+Ti), and titanium contentbecame 1% by atom, as atom number ratio represented by Ti/(In+Ce+Ti).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃ phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111), represented by the above equation (1), was 7%.

Density of the oxide sintered body was measured and found to be 7.06g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM (refer to FIG. 5), and found that average particlediameter of the CeO₂ phase was 1.1 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 400° C. to form a transparent conductive filmwith a film thickness of 200 nm. It was confirmed that the compositionof the resultant transparent conductive film was nearly the same as thatof the target.

By measurement of specific resistance of the film, it was found to be5.0×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 2.5×10²⁰ cm⁻³, and carrierelectron mobility was 50 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.16. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Example 4

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder was obtained, by adjusting indium oxide powder, cerium oxidepowder and titanium oxide powder to have an average particle diameter ofequal to or smaller than 1 μm, so that cerium content became 0.3% byatom, as atom number ratio represented by Ce/(In+Ce+Ti), and titaniumcontent became 0.3% by atom, as atom number ratio represented byTi/(In+Ce+Ti).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃ phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111), represented by the above equation (1), was 1%.

Density of the oxide sintered body was measured and found to be 7.05g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 1.0 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 300° C. to form a transparent conductive filmwith a film thickness of 200 nm. It was confirmed that the compositionof the resultant transparent conductive film was nearly the same as thatof the target.

By measurement of specific resistance of the film, it was found to be5.0×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 1.5×10²⁰ cm⁻³, and carrierelectron mobility was 83 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.12. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Example 5

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder was obtained, by adjusting indium oxide powder, cerium oxidepowder and zirconium oxide powder to have an average particle diameterof equal to or smaller than 1 μm, so that cerium content became 0.3% byatom, as atom number ratio represented by Ce/(In+Ce+Zr) , and zirconiumcontent became 0.3% by atom, as atom number ratio represented byZr/(In+Ce+Zr).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃ phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111), represented by the above equation (1), was 1%.

Density of the oxide sintered body was measured and found to be 6.98g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 1.0 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 300° C. to forma transparent conductive film witha film thickness of 200 nm. It was confirmed that the composition of theresultant transparent conductive film was nearly the same as that of thetarget.

By measurement of specific resistance of the film, it was found to be5.2×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 1.5×10²⁰ cm⁻³, and carrierelectron mobility was 80 CM²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.12. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium and zirconium to bein a solid solution state in the indium oxide phase.

It should be noted that nearly the same result was obtained, also in thecase where hafnium, molybdenum or tungsten was added in the samecomposition, instead of zirconium.

Reference Example 7

Film-formation was performed by changing a film-formation method to anion plating method using a tablet composed of an oxide sintered bodyhaving a cerium content of 2% by atom, as an atomicity ratio representedby Ce/(In+Ce).

A method for preparing the oxide sintered body was nearly the same as inthe case of the sputtering target of Reference Example 1, however, asdescribed above, in the case of using as the tablet for ion plating, itis necessary to decrease density, therefore, sintering temperature wasset as 1100° C. The tablet was molded in advance so as to attaindimension after sintering of a diameter of 30 mm and a height of 40 mm.Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of the In₂O₃ phasewith a bixbyite-type structure, and the CeO₂ phase with a fluorite-typestructure. X-ray diffraction peak intensity ratio of the CeO₂ phase(111), represented by the above equation (1), was 4%. Density of theoxide sintered body was measured and found to be 4.67 g/cm³.Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 1.0 μm.

Discharge was continued, using a plasma gun by an ion plating method,using such an oxide sintered body as the tablet, until the tablet becamenot usable. As an ion plating apparatus, a reactive plasma vapordeposition apparatus was used, where high density plasma assisted vacuumvapor deposition method (HDPE method) was applicable. As film-formationcondition, distance between an evaporation source and a substrate wasset at 0.6 m, discharge current of the plasma gun at 100 A, Ar flow rateat 30 sccm, and O₂ flow rate at 10 sccm. A problem of splash or the likedid not occur during a period until the tablet became not usable.

After replacing the tablet, film-formation was performed. It should benoted that substrate temperature was set at 300° C. to form atransparent conductive film with a film thickness of 200 nm. It wasconfirmed that the composition of the resultant transparent conductivefilm was nearly the same as that of the target.

By measurement of specific resistance of the film, it was found to be3.3×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 2.1×10²⁰ cm⁻³, and carrierelectron mobility was 92 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was 2.13. Crystallinity of the film was identified by X-raydiffraction measurement, and confirmed to be to be a crystalline filmcomposed of an indium oxide phase only, and cerium to be in a solidsolution state in the indium oxide phase.

Comparative Example 1

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder, adjusted to have an average particle diameter of equal to orsmaller than 1 μm, was prepared, so that cerium content became 0.1% byatom, as atom number ratio represented by Ce/(In+Ce).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of only the In₂O₃phase with a bixbyite-type structure.

Density of the oxide sintered body was measured and found to be 6.74g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and such an aspect was observed as quite a smallquantity of the CeO₂ phase was scattered about. Average particlediameter of the CeO₂ phase was 1.0 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencein direct-current sputtering was studied. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was also zero.

Subsequently, similarly as in Reference Example 1, film-formation wasperformed by direct-current sputtering. It should be noted thatsubstrate temperature was set at 300° C. to form a transparentconductive film with a film thickness of 200 nm. It was confirmed thatthe composition of the resultant transparent conductive film was nearlythe same as that of the tablet.

By measurement of specific resistance of the film, showing as high valueas 1.3×10⁻³ Ω·cm. In addition, measurement of hole effect was performedand found that carrier electron concentration was 6.2×10²⁰ cm⁻³, andcarrier electron mobility was 68 cm²V⁻¹s⁻¹. Refractive index of awavelength of 460 nm was 2.12. Crystallinity of the film was identifiedby X-ray diffraction measurement, and confirmed to be to be acrystalline film composed of an indium oxide phase only, and cerium tobe in a solid solution state in the indium oxide phase.

Comparative Example 2

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder, adjusted to have an average particle diameter of equal to orsmaller than 1.5 μm, was prepared, so that cerium content became 11% byatom, as atom number ratio represented by Ce/(In+Ce).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of only the In₂O₃phase with a bixbyite-type structure, and the CeO₂ phase of afluorite-type structure. X-ray diffraction peak intensity ratio of theCeO₂ phase (111), represented by the above equation (1), was as high as28%.

Density of the oxide sintered body was measured and found to be a littlelower value of 6.69 g/cm³. Subsequently, texture observation of theoxide sintered body was performed with SEM, and found that averageparticle diameter of the CeO₂ phase was 2.6 μm. In addition, such anaspect was observed as crystal grains of the In₂O₃ phase were convertedto a little fine size, which was estimated to be caused by increase involume ratio of crystal grains of the CeO₂ phase. It is considered that,in this way, X-ray diffraction peak intensity ratio of the CeO₂ phase(111) expressed by the above formula (1), became high.

Next, by a similar method as in Reference Example 1, arcing occurrencein direct-current sputtering was studied. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was also zero.

Subsequently, similarly as in Example 1, film-formation was performed bydirect-current sputtering. It should be noted that substrate temperaturewas set at 500° C. to forma transparent conductive film with a filmthickness of 200 nm. It was confirmed that the composition of theresultant transparent conductive film was nearly the same as that of thetablet.

By measurement of specific resistance of the film, showing as high valueas 1.0×10⁻³ Ω·cm. In addition, measurement of hole effect was performedand found that carrier electron concentration was 2.8×10²⁰ cm⁻³, andcarrier electron mobility was 21 cm²V⁻¹s⁻¹. Refractive index of awavelength of 460 nm was 2.18. Crystallinity of the film was identifiedby X-ray diffraction measurement, and confirmed to be to be acrystalline film composed of an indium oxide phase only, and cerium tobe in a solid solution state in the indium oxide phase.

Comparative Example 3

An oxide sintered body along with a sputtering target was prepared by asimilar method as in Reference Example 1, except that cerium oxidepowder with an average particle diameter of 2 μm was used as rawmaterial powder.

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and confirmed to be composed of only the In₂O₃phase with a bixbyite-type structure, and the CeO₂ phase of afluorite-type structure. X-ray diffraction peak intensity ratio of theCeO₂ phase (111) , represented by the above equation (1), was as high as18%.

Density of the oxide sintered body was measured and found to be 6.72g/cm³. Subsequently, texture observation of the oxide sintered body wasperformed with SEM, and found that average particle diameter of the CeO₂phase was 4.2 μm.

Next, by a similar method as in Reference Example 1, arcing occurrencein direct-current sputtering was studied. Direct-current sputtering wasperformed till attaining a cumulative charge power value of 12.8 KWh.Arcing did not generate for a while after starting the sputtering,however, after elapsing of a cumulative time for 11.2 kWh, arcinggenerated increasingly. After attaining the cumulative time, the targetsurface was observed to confirm generation of many nodules.Subsequently, by changing direct-current power to 200, 400, 500 and 600W, sputtering was performed for 10 minutes under each power to measurearcing occurrence number of times. In FIG. 3, average arcing occurrencenumber of times per minute at each direct-current power was shown,together with Example 2. From FIG. 3, it is clear that arcing generatedfrequently with increase in direct-current power. It should be notedthat film-formation was not performed because of frequent occurrence ofarcing.

Comparative Example 4

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder was obtained, by adjusting indium oxide powder, cerium oxidepowder and titanium oxide powder to have an average particle diameter ofequal to or smaller than 1 μm, so that cerium content became 0.3% byatom, as atom number ratio represented by Ce/(In+Ce+Ti) , and titaniumcontent became 3% by atom, as atom number ratio represented byTi/(In+Ce+Ti).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and the diffraction peak derived from only theIn₂O₃ phase with a bixbyite-type structure was observed, and thediffraction peak derived from the CeO₂ phase with a fluorite-typestructure was not observed. Density of the oxide sintered body wasmeasured and found to be 7.04 g/cm³.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 300° C. to form a transparent conductive filmwith a film thickness of 200 nm. It was confirmed that the compositionof the resultant transparent conductive film was nearly the same as thatof the target.

By measurement of specific resistance of the film, it was found to be3.0×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 5.6×10²⁰ cm⁻³, and carrierelectron mobility was 37 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was as low as 2.07. Crystallinity of the film was identified byX-ray diffraction measurement, and confirmed to be to be a crystallinefilm composed of an indium oxide phase only, and cerium and titanium tobe in a solid solution state in the indium oxide phase.

Comparative Example 5

An oxide sintered body along with a sputtering target were prepared by asimilar method as in Reference Example 1, except that raw materialpowder was obtained, by adjusting indium oxide powder, cerium oxidepowder and tin oxide powder to have an average particle diameter ofequal to or smaller than 1 μm, so that cerium content became 0.3% byatom, as atom number ratio represented by Ce/(In+Ce+Sn) , and tincontent became 3% by atom, as atom number ratio represented bySn/(In+Ce+Sn).

Composition analysis of the resultant oxide sintered body was performedby an ICP emission spectrometry, and it was confirmed to be nearly thesame as charging composition in blending raw material powder. Next,phase identification of the oxide sintered body was performed by X-raydiffraction measurement, and the diffraction peak derived from only theIn₂O₃ phase with a bixbyite-type structure was observed, and thediffraction peak derived from the CeO₂ phase with a fluorite-typestructure was not observed. Density of the oxide sintered body wasmeasured and found to be 7.09 g/cm³.

Next, by a similar method as in Reference Example 1, arcing occurrencewas studied in direct-current sputtering. Arcing did not generate tillattaining a cumulative charge power value of 12.8 KWh, and discharge wasstable. In addition, in the case of changing direct-current power,arcing occurrence number of times per minute under each direct-currentpower was zero.

Subsequently, film-formation was performed by direct-current sputtering,similarly as in Reference Example 1. It should be noted that substratetemperature was set at 300° C. to forma transparent conductive film witha film thickness of 200 nm. It was confirmed that the composition of theresultant transparent conductive film was nearly the same as that of thetarget.

By measurement of specific resistance of the film, it was found to be2.6×10⁻⁴ Ω·cm. In addition, measurement of hole effect was performed andfound that carrier electron concentration was 7.3×10²⁰ cm⁻³, and carrierelectron mobility was 33 cm²V⁻¹s⁻¹. Refractive index of a wavelength of460 nm was as low as 2.04. Crystallinity of the film was identified byX-ray diffraction measurement, and confirmed to be to be a crystallinefilm composed of an indium oxide phase only, and cerium and tin to be ina solid solution state in the indium oxide phase.

TABLE 1 CeO₂ phase Average Ce/(In + M/(In + Main Second (111)/ particleSintered Specific Ce + M) Ce + M) phase of phase of In₂O₃ diameter bodyresistance Refrac- Ce/(In + Ce) M (% by (% by sintered sintered phase ofCeO₂ density (×10⁻⁴ tive (% by atom) element atom) atom) body body (222)phase (μm) (g/cm³) Arcing Ω · cm) index Reference 9 — — — bixbyite-Fluorite- 16%  1.1 6.87 None 6.6 2.21 Example 1 type In₂O₃ type CeO₂Reference 7 — — — phase phase 14%  2.7 6.88 5.4 2.20 Example 2 Reference5 — — — 9% 1.3 6.92 4.6 2.19 Example 3 Reference 4 — — — 8% 2.8 6.91 4.22.17 Example 4 Reference 1 — — — 2% 1.1 6.86 4.4 2.14 Example 5Reference 0.3 — — — 0.5%  1.2 6.70 7.6 2.13 Example 6 Example 1 — Ti 8 125%  2.7 7.06 5.6 2.14 Example 2 — Ti 5 0.5 14%  1.5 7.01 5.4 2.17Example 3 — Ti 4 1 7% 1.1 7.06 5 2.16 Example 4 — Ti 0.3 0.3 1% 1.0 7.055 2.12 Example 5 — Zr 0.3 0.3 1% 1.0 6.98 5.2 2.12 Reference 2 — — — 4%1.0 4.67 3.3 2.13 Example 6 Comparative 0.1 — — — — — 1.0 6.74 13 2.12Example 1 Comparative 11 — — — Fluorite- 28%  2.6 6.69 10 2.18 Example 2type CeO₂ Comparative 9 — — — phase 18%  4.2 6.72 Yes — — Example 3Comparative — Ti 0.3 3 — — — 7.04 None 3 2.07 Example 4 Comparative — Sn0.3 3 — — — 7.09 2.6 2.04 Example 5(Evaluation)

From the result shown in Table 1, in Reference Examples 1 to 7, theoxide sintered bodies (the first oxide sintered bodies) composed of anindium oxide and a cerium oxide were prepared, by using indium oxidepowder and cerium oxide powder adjusted to have an average particlediameter of equal to or smaller than 1.5 μm, to blend in a range of acerium content of 0.3 to 9% by atom, as an atomicity ratio ofCe/(In+Ce), and it was confirmed that the oxide sintered bodies had asintered body texture having the In₂O₃ phase of a bixbyite-typestructure, as a main crystal phase, finely dispersed with a CeO₂ phaseof a fluorite-type structure, as a second phase, as crystal grainshaving an average particle diameter of equal to or smaller than 3 μm.Still more, it was confirmed that, as for relation between particlediameter and a dispersed state of the crystal grains of the In₂O₃ phaseand the CeO₂ phase, X-ray diffraction peak intensity ratio of the CeO₂phase (111) relative to the In₂O₃ phase (222) is equal to or lower than25%.

In addition, in Examples 1 to 5, it was confirmed that the oxidesintered bodies were prepared, which contained indium, cerium and the Melement as oxides, by using the indium oxide powder and the cerium oxidepowder, and oxide powder of at least one or more kinds of the M elementselected from the metal element group consisting of titanium, zirconium,hafnium, molybdenum and tungsten, adjusted to have an average particlediameter of equal to or smaller than 1.5 μm, and blending them in arange of the cerium content of 0.3 to 9% by atom, as an atomicity ratioof Ce/(In+Ce), the M element content of equal to or lower than 1% byatom, as an atomicity ratio of M/(In+Ce+M), and the total content ofcerium and the M element of equal to or lower than 9% by atom, as anatomicity ratio of (Ce+M)/(In+Ce+M); and they had a finely dispersedtexture similar to that of the oxide sintered bodies of ReferenceExamples 1 to 6.

The oxide sintered bodies of Examples 1 to 5 all showed such highdensity as a density of the sintered body of equal to or higher than 6.3g/cm³. When these oxide sintered bodies were used as a sputtering targetto perform direct-current sputtering, it was clarified that, even aftercontinuous sputtering for a long period of time, generation of a nodulestarted from a digging residue of sputtering caused by the CeO₂ phasewas not observed, and even when direct-current power was changed withina range of 200 to 600 W, arcing did not generate.

It was confirmed that specific resistance of the crystalline transparentconductive films formed in Examples 1 to 5 was as good as equal to orlower than 8×10⁻⁴ Ω·cm, and this low specific resistance depends on highcarrier electron mobility over 35 cm²V⁻¹s⁻¹. At the same time, as foroptical characteristics, it was confirmed that, because of suppressionof the carrier electron concentration to a low level, refractive indexin a wavelength of 460 nm showed such high value as over 2.1. It shouldbe noted that, in Example 3, refractive index in a wavelength of 460 nmshowed such high value as over 2.1, although the carrier electronmobility was low because of being amorphous.

As compared with Examples 1 to 5, in Comparative Example 1, the ceriumcontent is set at 0.1% by atom, as an atomicity ratio of Ce/(In+Ce),outside the range of the present invention. Because of too low ceriumcontent, the crystalline transparent conductive film formed was not ableto attain sufficient carrier electron concentration, and showed aspecific resistance of 1.3×10⁻³Ω−cm, not attaining the level of equal toor lower than 8×10⁻⁴ Ω·cm, required in applications of a blue LED or asolar cell and the like.

Similarly, in Comparative Example 2, the cerium content is set at 11% byatom, as an atomicity ratio of Ce/(In+Ce), outside the range of thepresent invention. Because of too high cerium content, the crystallinetransparent conductive film formed had low carrier electron mobility,and showed a specific resistance of 1.0×10⁻³ Ω·cm, not attaining thelevel of equal to or lower than 8×10⁻⁴Ω·cm, required in applications ofa blue LED or a solar cell and the like.

As compared with Examples 1 to 5, in Comparative Example 3, because ofusing relatively coarse cerium oxide powder having a average particlediameter of 2 μm, as raw material powder, average particle diameter ofthe crystal grain composed of the CeO₂ phase dispersed in the oxidesintered body was over 3 μm. When direct-current sputtering wasperformed using the oxide sintered body having such a texture as asputtering target, it was confirmed that nodules generated and arcinggenerated frequently after continuous sputtering for a long period oftime. That is, it was clarified that, as in Reference Examples 1 to 11,the texture of the oxide sintered body, having the finely dispersedcrystal grains composed of the CeO₂ phase, so as to have an averageparticle diameter of equal to or smaller than 3 μm, by using the ceriumoxide powder adjusted to have an average particle diameter of equal toor smaller than 1.5 μm, is effective to suppress nodule generation andarcing generation.

As compared with Examples 1 to 5, in Comparative Example 4, the titaniumcontent is set at 3% by atom, as an atomicity ratio of Ti/(In+Ce+Ti),outside the range of the present invention. Because of too high titaniumcontent, the crystalline transparent conductive film formed had too highcarrier electron concentration, and showed a refractive index of 2.07,not attaining the level of 2.1, required in applications of a blue LEDand the like.

The oxide sintered body of Comparative Example 5 contains tin differentfrom the composition element of the oxide sintered body of the presentinvention, with the tin content of 3% by atom, as an atomicity ratio ofSn/(In+Ce+Sn), other than indium and cerium. Because of containing tin,the crystalline transparent conductive film formed had too high carrierelectron concentration, and showed a refractive index of 2.04, notattaining the level of 2.1, required in applications of a blue LED andthe like.

INDUSTRIAL APPLICABILITY

The oxide sintered body containing indium, cerium and the M element, ofthe present invention, may be used in producing the oxide transparentconductive film by sputtering method. This transparent conductive filmis extremely useful industrially as a surface electrode for a blue LED(Light Emitting Diode) or a solar cell, and as a high refractive indexfilm for an optical disk.

The invention claimed is:
 1. An oxide sintered body comprising: anindium oxide; a cerium oxide, and an oxide of at least one metal element(M element) selected from the group consisting of titanium, zirconium,hafnium, molybdenum and tungsten, wherein the cerium content is 0.3 to9% by atom, as an atomicity ratio of Ce/(In+Ce+M), the M element contentis equal to or lower than 1% by atom, as an atomicity ratio ofM/(In+Ce+M), and the total content of cerium and the M element is equalto or lower than 9% by atom, as an atomicity ratio of (Ce+M)/(In+Ce+M),and wherein said oxide sintered body comprising an In₂O₃ phase of abixbyite structure as a main crystal phase, a CeO₂ phase of afluorite-type structure finely dispersed as crystal grains having anaverage particle diameter of equal to or smaller than 3 μm, as a secondphase.
 2. The oxide sintered body according to claim 1, wherein X-raydiffraction peak intensity ratio (I), defined by the following formula,is equal to or lower than 25%:I=[CeO₂ phase (111)/In₂O₃ phase (222)]×100[%].
 3. The oxide sinteredbody according to claim 1, wherein the M element is titanium.
 4. Theoxide sintered body according to claim 1, wherein the oxide sinteredbody does not contain tin.
 5. A production method for the oxide sinteredbody of claim 1, comprising: adding and mixing oxide powder of at leastone or more kinds of an M element selected from the M metal elementgroup consisting of titanium, zirconium, hafnium, molybdenum andtungsten, to raw material powder comprising indium oxide powder andcerium oxide powder, and then (i) molding the mixed powder, andsintering the molding by a normal pressure sintering method, or (ii)molding and sintering the mixed powder by a hot press method, whereinaverage particle diameter of the raw material powder is adjusted toequal to or smaller than 1.5 μm, that the oxide sintered body aftersintering has an In₂O₃ phase of a bixbyite-type structure, as a maincrystal phase, and a CeO₂ phase of a fluorite-type structure finelydispersed as crystal grains having an average particle diameter of equalto or smaller than 3 μm, as a second phase.
 6. The production method forthe oxide sintered body according to claim 5, wherein the oxide sinteredbody is obtained by sintering the molding by a normal pressure sinteringmethod, under atmosphere containing oxygen gas, at a sinteringtemperature of 1250 to 1650° C., for a sintering time of 10 to 30 hours.7. The production method for the oxide sintered body according to claim5, wherein the oxide sintered body is obtained by molding and sinteringthe mixed powder by a hot press method, at a temperature of 700 to 950°C. for 1 to 10 hours, under a pressure of 2.45 to 29.40 MPa, under inertgas atmosphere or in vacuum.
 8. The oxide sintered body according to anyone of claims 1 to 4, wherein density of the oxide sintered body isequal to or higher than 6.3 g/cm³.